Topic: yet another 400 problem

[muttblbc]

so i just finished an engine rebuild, i got everything back on the bike and it wont start. its got compression, spark, but when i pull the plugs out theyre clean and dry so obviously im not getting gas. ive been through the carbs 3 times and theyre clean as a whistle. i put my hands on the carb intakes as i crank the engine and i can feel the vacuum as well as get gas on my hands. ive been pulling my hair out all day and im sure its a simple thing im overlooking but.... anyone?

[Triffecpa]

hit it with starter fluid.  If it'll pop off, then you have a fuel problem.  If it still won't run, you either have an electrical or timing problem.

TR

[Bodi]

carb slides reversed? yours acts like mine did when I did that...

[Kevin400F]

Any progress yet?   It sounds like you verified you have a fat blue spark by laying a plug againsnt the engine, but is the ignition timing spot-on as well? The plugs should fire at the "F" mark.  I've seen instances where folks inadvertently set the timing at the "T", or even at the "double line" full advance mark. 

Do you have points, or has it been converted to electronic ignition?  As a down-and-dirty check, a 12V light bulb connected across the point contacts should just come on as the engine is turned forward by hand to their respective "F" mark.  Also, make sure your coil wires are running to the proper cylinders, and that the 1-4 coil is connected to the 1-4 points (similarly 2-3 coil to 2-3 points.

[muttblbc]

timings as dead on as you can get it statically, plug wires are routed right, shes turning over but not catching and theres still no gas on the plugs. i did get her to backfire once or twice when i was spinning the crank by hand while setting the timing if that tells you anything.

[Gordon]

Check to make sure you haven't switched the yellow and blue wires either at the points or the coils.

Have you opened the float bowl drain screws to verify you have gas in all four carbs?

[Tim2005]

How did you set the valve timing when you rebuilt the motor? Also, what did the engine rebuild involve?

[mattcb350f]

i put my hands on the carb intakes as i crank the engine and i can feel the vacuum as well as get gas on my hands.

Did you get the gas on your hands because of blow back out the carbs? This might happen if you set the valve adjustment too tight and the valves are being held open a wee bit. Even if you set them, check again. They may have tightened up since you tried starting the bike 

Matt.

[muttblbc]

thanks for all the advice, so for those of you who dont know, you cant rejet a set of 350 carbs and have them work on a 400. i guess that would be a big duh, but it all looked alright when i compared them in my service specs manual. once again the people on this forum are awesome thanks for the help.

[Kevin400F]

So, are you trying to say that the engine wouldn't start simply because the carbs started out as CB350F carbs?   While the jetting, needle profile etc. might not have been "ideal", it is close enough that the engine absolutely should have started.   It sounds like you either have plugged slow jets or plugged passages in the carbs.

[Gordon]

thanks for all the advice, so for those of you who dont know, you cant rejet a set of 350 carbs and have them work on a 400.

Actually, you can.  The carbs are the same except for the jets.  I swapped carbs between my 350 and 400 a few times with no issues at all. 

[muttblbc]

weird, i went through those carbs twice. ultrasoniced them and blew out all the jets and passages with compressed air, and the thing would not work but fired right up with a set of 400 carbs and using the same jets that i had put into 350s.

[tomkimberly]

Did you put the retainer clips on upside down? When installed wrong they keep the fuel seat stuck closed. I know because I've done it myself.

Tom